There are only so many people on earth, and so many hours in the day. Is that starting to limit the growth of social media?

Think about how much time you, and the people around you, spend on social networks every day. Ask yourself: how much more time could you possibly spend on Facebook, Snapchat, and Twitter without losing your job entirely? Probably not much.

And in the developed world, at least, there aren’t many people left who aren’t already on social media, meaning there’s potentially not much room for growth.

Facebook revealed late last month that its number of users in the United States was flat from earlier this year and that its users in Europe had fallen over the same period, even though its total number of members had grown. And Twitter, which has struggled for years to increase interest in its platform, also said in late July that its monthly active users had decreased by one million from earlier this year. After those disclosures, share prices of both Facebook and Twitter tumbled.

The declines and flattening growth raise questions about whether the social media companies have reached a saturation point in some markets, especially in developed countries.

“And Alexander wept, for there were no more worlds to conquer.”

It hardly seems like a problem, right? They’ve taken up so much human attention that there isn’t any left to capture!

But companies built around the assumption of perpetual growth don’t think that way, so you can bet these companies will dream up new ways to grab more attention from more people. You’ll have to decide if you want to give them that, or if they’ve had enough.